Wireless communications within mm-wave bands (28, 38, 60, 73 GHz, and beyond) attract growing interest due to the diminishing availability of open spectrum in lower frequency bands. One of the recognized benefits of mm-wave communications is the opportunity to employ electrically large antenna arrays to overcome the attenuation and blockage challenges in wide area operation. Unfortunately, the cost and power consumption of mm-wave mixed signal analog/digital components can make it prohibitively expensive to utilize an RF chain and analog-to-digital/digital-to-analog converter (ADC/DAC) for each of the antenna elements in a large array to enable multiple-input/multiple-output (MIMO) signal processing in the baseband. Novel architectures capable of simultaneously addressing the challenges of cost and power have the potential for broad impact in the next generation of wireless systems.